Field of the Invention
The present invention relates to an image capturing apparatus including a focus detection pixel in an image sensor.
Description of the Related Art
In recent years, image capturing equipment such as household video cameras and digital still cameras have come into common use. They are also equipped with an auto-focus (AF) function that automatically sets the lens focus position, and the user can perform imaging while leaving focusing up to the camera instead of adjusting the focus theirself, making it a function that is beneficial to the user.
AF mechanisms that use an image sensor are largely split into two types according to their structure, namely a contrast AF system and an on-imaging surface phase difference AF system. The contrast AF system performs filter processing on output from normal image forming pixels, and while driving a focus lens, searches for a position with the largest filter output, and obtains the focus position. This system is simply configured, but there is an issue of time being required.
On the other hand, in the on-imaging surface phase difference AF system, focus detection dedicated pixels are provided in the image sensor, a defocus amount is obtained from the difference in output from the pixels dedicated to focus detection, and a focus position is obtained. This system obtains a defocus amount from one image frame, and therefore has the merit of requiring very little time. If the on-imaging surface phase difference AF technique is used, continuous setting of the focus position during continuous shooting is possible without reducing the continuous shooting speed.
For example, in Japanese Patent Laid-Open No. 2009-109631, the focus position is obtained from the focus detection dedicated pixels of an image captured during continuous shooting, and the continuous shooting speed is improved by performing lens driving during readout.
Also, it is disclosed in Japanese Patent Laid-Open No. 2010-219958 that to improve the S/N ratio of the signals from the focus detection pixels, charge storage is performed independently for imaging pixels and focus detection pixels, image data is thinned out and read out, and then signals are read out from the focus detection pixels arranged in the rows that were thinned out.
However, in the method in the above-mentioned Japanese Patent Laid-Open No. 2009-109631, there is an issue of a limit on acceleration of the continuous shooting speed because pixels are read out in succession from the top of the angle of view and therefore a focus position cannot be obtained until readout of the focus detection dedicated pixels has been completed. Also, it is disclosed in Japanese Patent Laid Open No. 2010-219958 that signals from the focus detection pixels are read out together, but no consideration has been given to improving the continuous shooting speed.